Secondary 4 Pure Biology Practice Paper 1

TuitionGoWhere Practice Paper - Pure Biology Secondary 4 (Answer Key)

TuitionGoWhere Practice Paper (AI) - Marking Scheme

Total Marks: 80

Section A [40 marks]

1. Cell Structure and Specialization [12 marks]

(a) Name the structures [4 marks - 1 mark each]

• A: Chloroplast ✓
• B: Nucleus ✓
• C: Cell wall ✓
• D: Vacuole ✓

(b) Function of structure A [2 marks] Site of photosynthesis ✓ / converts light energy to chemical energy ✓ Accept: makes glucose, contains chlorophyll

(c) Adaptation of structure F [2 marks] Small size allows it to fit in cytoplasm ✓ / can be attached to rough ER for protein synthesis ✓ Accept: made of RNA and protein for function, can be free or bound

(d) Two differences from animal cell [4 marks - 2 marks each]

1. Plant cell has cell wall ✓ animal cell has no cell wall ✓
2. Plant cell has large permanent vacuole ✓ animal cell has small temporary vacuoles ✓ Also accept: chloroplasts present/absent, different shape

2. Transport Mechanisms [15 marks]

(a) Process name [1 mark] Osmosis ✓

(b) Graph plotting [4 marks]

• Correct axes labeled with units ✓
• Appropriate scale using most of grid ✓
• All points plotted correctly ✓
• Smooth curve through points ✓

(c) Isotonic concentration [1 mark] 0.4 mol/dm³ ✓

(d) Explanation for mass gain [3 marks] Water potential of pure water is higher than cell sap ✓ water moves into cells by osmosis ✓ cells become turgid causing tissue to swell ✓

(e) Microscopic changes in 1.0 mol/dm³ [3 marks] Water moves out of cells by osmosis ✓ cell membrane pulls away from cell wall ✓ plasmolysis occurs ✓

(f) Effect of higher temperature [3 marks] Molecules have more kinetic energy ✓ rate of osmosis increases ✓ changes in mass would occur faster/be greater ✓ Accept: enzyme activity increases, cell membrane more permeable

3. Enzyme Activity [13 marks]

(a) Optimum pH values [2 marks - 1 mark each]

• Pepsin: pH 2 ✓
• Trypsin: pH 8 ✓

(b) Different optimum pH explanation [3 marks] Enzymes have different amino acid sequences ✓ which determine their 3D structure ✓ active site shape is maintained at different pH values ✓ Accept: different protein structure, evolved for different environments

(c) Effect of pH change [3 marks] Hydrogen ions affect ionic bonds in enzyme ✓ enzyme changes shape/denatures ✓ active site no longer complementary to substrate ✓

(d) Relation to digestive system [3 marks] Stomach is acidic (pH 1-2) ✓ suitable for pepsin activity ✓ small intestine is alkaline (pH 8-9) suitable for trypsin ✓

(e) Effect of stomach pH 7 [2 marks] Pepsin would be denatured/inactive ✓ protein digestion would be reduced/stopped ✓

Section B [40 marks]

4. Photosynthesis and Limiting Factors [20 marks]

(a) Relationship at 25°C [3 marks] Rate increases with light intensity up to about 800 units ✓ then levels off/remains constant ✓ showing light is initially limiting then another factor becomes limiting ✓

(b) Comparison of temperatures [4 marks] Both show similar pattern of increase then leveling off ✓ rate at 25°C is higher than at 15°C at all light intensities ✓ both level off at high light intensities ✓ 25°C reaches higher maximum rate ✓

(c) Explanation for leveling off [3 marks] Light is no longer the limiting factor ✓ CO₂ concentration or temperature becomes limiting ✓ rate cannot increase further without increasing the limiting factor ✓

(d) Ways to increase rate at point X [2 marks - 1 mark each]

1. Increase CO₂ concentration ✓
2. Increase temperature ✓ Also accept: add more chlorophyll, increase water availability

(e) Balanced equation [2 marks] 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ ✓✓ Award 1 mark for correct reactants and products, 1 mark for balancing

(f) Importance of photosynthesis [6 marks] Produces glucose which is food for plants ✓ plants are eaten by animals providing energy ✓ forms basis of all food chains/webs ✓ produces oxygen for aerobic respiration ✓ removes CO₂ from atmosphere ✓ without photosynthesis most life would not exist ✓ Accept any 6 valid points about energy flow, oxygen production, carbon cycle

5. Homeostasis and Blood Glucose Regulation [20 marks]

(a) Changes in blood glucose [3 marks] Increases rapidly after meal to peak ✓ then decreases gradually ✓ returns to normal level after about 4 hours ✓

(b) Hormone name [1 mark] Insulin ✓

(c) Organ producing hormone [1 mark] Pancreas ✓

(d) How hormone decreases glucose [4 marks] Insulin binds to receptors on liver cells ✓ stimulates conversion of glucose to glycogen ✓ glycogen stored in liver ✓ glucose removed from blood for storage ✓ Also accept: increases glucose uptake by cells, stimulates respiration

(e) Negative feedback explanation [3 marks] High blood glucose detected by pancreas ✓ insulin released which lowers glucose ✓ response opposes original stimulus returning system to normal ✓

(f) Managing Type 2 diabetes [4 marks] Regular exercise to increase glucose uptake by muscles ✓ reduce carbohydrate intake in diet ✓ eat smaller more frequent meals ✓ maintain healthy body weight ✓ Accept: avoid sugary foods, increase fiber intake, monitor blood glucose

(g) Similarities with temperature regulation [4 marks - 2 marks each]

1. Both involve negative feedback ✓ to maintain constant internal environment ✓
2. Both have control center that detects changes ✓ and coordinates response through effectors ✓ Also accept: both maintain homeostasis, both involve hormones, both have set points

Marking Guidelines:

• Award marks for scientifically accurate alternative expressions
• Accept correct scientific terminology and abbreviations
• Look for understanding of concepts rather than exact wording
• Deduct marks for factual errors
• Award partial marks for incomplete but correct responses

Grade Boundaries (Suggested):

• A: 72-80 marks (90-100%)
• B: 64-71 marks (80-89%)
• C: 56-63 marks (70-79%)
• D: 48-55 marks (60-69%)
• E: 40-47 marks (50-59%)